The present invention relates to compositions for use as a processing aid in recovering lactose from whey by filtration and evaporation. More particularly, it relates to such compositions composed of sodium hexametaphosphate having polyphosphate chain lengths of 12 to 28 in combination with tetrasodium or tetrapotassium pyrophosphate or a blend of sodium hexametaphosphate wherein the hexametaphosphate is comprised of polyphosphates with a chain length range of 12 to 14 in one instance and 12 to 28 in another.
When calcium and magnesium are present in aqueous solutions, their salts tend to precipitate out of solution onto the surfaces of processing equipment. The salts of calcium and magnesium, especially the carbonate and phosphate salts, become less soluble with increasing temperature, pressure, and pH. The amount of calcium present in whey and/or dairy products can pose a major problem in processing these types of products. As these products come in contact with heated surfaces such as those found in heat exchangers, pasteurizers, and evaporators, the calcium salts become insoluble and create a scale that reduces heat transfer efficiency. In time, this type of scale can become so heavy that it can plug the tubes of an evaporator, the plates of a pasteurizer, and the pores of a filter membrane. Scale build-up equates to shorter production runs, higher energy costs, and more time and chemicals required for cleaning.
Polyphosphates function to prevent excess scale formation by a phenomenon known as the "Threshold Effect". The Threshold Effect is the prevention of precipitation from supersaturated solutions of scalants, such as calcium carbonate and calcium phosphate, by sub-stoichiometric levels of inhibitor. This means that very small doses (ppm levels) of phosphate sequestrants can effectively prevent precipitate formation from solutions that contain large amounts of scalants. Present mechanistic theories postulate that the threshold agent is adsorbed on the growth sites of the scalant crystallite during the process of crystallization. This adsorption alters the growth pattern so that the resultant scalant crystals are formed more slowly and are highly distorted. Obviously, the retardation of crystal growth rate would lower the amount of solid deposited on surfaces needed to be kept scale-free. Secondly, the distortion of crystal structure offers the possibility of different adherence characteristics of that solid formed so that surfaces could have a lower degree of scaling. As previously stated, phosphate sequestrants function to retard scale formation, they do not prevent it.
The use of phosphates in the processing of whey is well known. In U.S. Pat. No. 2,467,453 it is stated that trisodium phosphate, sodium hexametaphosphate, and sodium pyrophosphate are known for stabilizing whey protein. U.S. Pat. No. 4,342,604 discloses hexametaphosphate chain lengths of up to 24 for processing cheese whey to obtain a lactose product. In U.S. Pat. No. 4,342,604 alkali metal polyphosphates having average chain lengths of 2 to 24 are employed to crystallize a lactose product from a cheese whey permeate.
While the use of the previously indicated phosphates have been successfully employed, there is a need for an improved composition and method which can result in a lower ash content for the lactose recovered from cheese whey and, at the same time, more effectively inhibit calcium scale build-up on surfaces of processing equipment and enhance its removal. Further, there is also a need for an improved composition and method which provides chelation of metal ions over a broader pH range as well as the production of more uniform whey and/or lactose crystals. Thus, the need exists for a more efficient composition and method of processing cheese whey and products derived thereof.